1. Field of the Invention
The present invention relates to stereoscopic image display devices, and in particular, to stereoscopic image display devices capable of displaying images stereoscopically to viewers in a plurality of different viewing positions without requiring stereoscopic image-viewing assist glasses.
2. Description of the Background Art
Generally, stereoscopic image display devices employ a method that presents images having a parallax to the left and right eyes of a viewer, respectively. As methods for presenting parallax images, it is possible to employ glasses for limiting light of images that enters the left and right eyes, respectively. However, it is also possible for a naked-eye viewing method that controls light of images that enters the left and right eyes of the viewer, without using such glasses.
In the case of the method using glasses, the viewer needs to wear glasses when viewing images. Therefore, the viewer may feel uncomfortable in wearing these glasses. On the other hand, in the case of the naked-eye viewing method which does not use glasses, it is general that stereoscopic image display devices employ a method using optical techniques such as a lenticular system or a parallax barrier system.
The lenticular system is a system in which an image is displayed by using a screen having a directivity in the horizontal direction (lenticular lens array), such that parallax images simultaneously enter the left and right eyes. The lenticular system has a problem that since a right eye image and a left eye image are displayed in alternating vertical pixel lines, the number of pixels in the vertical direction is halved.
The parallax barrier system is a system in which slits arranged between parallax display images and the eyes of the viewer serve as barriers for different parallax images such that a left parallax image and a right parallax image are generated, thereby causing the parallax images to simultaneously enter the left and right eye to display an image.
The parallax barrier system also has a problem that since a right eye image and a left eye image are displayed in alternating vertical pixel lines, the number of pixels in the vertical direction is halved. Moreover, since slits are used, the light utilization rate is also reduced.
A technique that solves the reduction of the number of pixels and the light utilization rate is proposed in International Publication WO 2004/027492, which discloses a configuration including: light sources arranged on light-incident surfaces at facing ends of a light guide plate; a prism sheet having a triangular prism row provided on a surface facing the light-emitting surface of the light guide plate, the triangular prism row extending in parallel to the light-incident surface of the light guide plate, and a cylindrical lens row provided on a surface opposite to the light-emitting surface of the light guide plate relative to the triangular prism row, the cylindrical lens extending in parallel to the triangular prism row; and a transmission-type liquid crystal panel arranged on the light-emitting surface of the prism sheet. A driving means causes light from the light sources to be emitted from the transmission-type display panel at an angle corresponding to the parallax between the left and right parallax, synchronized with the left and right parallax images to be alternately displayed on the transmission-type panel. International Publication WO 2004/027492 asserts that, according to the above configuration, a high-quality stereoscopic image can be obtained without reducing the number of pixels and the light utilization rate.
As also described in International Publication WO 2004/027492, within the lenticular lens system, an image is displayed through a lenticular lens in both cases where a two-dimensional image is displayed and where a stereoscopic image is displayed. In the parallax barrier system, in both cases where a two-dimensional image is displayed and where a stereoscopic image is displayed, such an image is displayed with a fixed parallax barrier. Alternatively, in the parallax barrier system, when a stereoscopic image is displayed, a display element such as a liquid crystal element is caused to function as a parallax barrier, and when a two-dimensional image is displayed, the image is allowed to pass through the display element without a parallax barrier. Moreover, in the configuration of the invention of International Publication WO 2004/027492, when a two-dimensional image is displayed, the left and right light sources are simultaneously lit.